This invention relates to a cassette for video, audio, or other tape, in which the tape is unwound from a feed reel and wound on a takeup reel, and more particularly to driven ribs projecting inwardly from the surrounding wall of the center hub opening of each such reel.
Conventionally, video and other tape cassettes are equipped with a front cover, known as a lid, at the front opening of the cassette housing. When the cassette is not in use, the lid closes the opening under the urging of a spring to protect the otherwise exposed tape portion with the front covering. This prevents intrusion of dust and dirt from the front into the opening, and also provides protection against fingerprinting due to careless handling, damaging, or oil staining. Without the protection, erroneous signals, disturbed video pictures in the case of a video tape, or dropout errors of audio tape could result. Even with the protection, however, the bottom of the front end of the cassette housing remains partly open, to be ready for tape loading or for other reasons. This condition lasts while the cassette is not in use. Accordingly, the ingress of dust from the bottom of the opening is not interrupted. Such a structure, if directly applied to the construction of video tape cassettes and the like, would cause serious errors because video signals are most susceptible to dust and dirt. With video cassettes, therefore, the dustproofness of the opening bottom has been an urgent problem to be settled. As an approach to the problem a mechanism has already been developed as illustrated by an exploded perspective view in FIG. 2. Numeral 10 designates an upper half housing part, 12 a lower half housing part, and 14 a front lid. They are assembled together to provide an enclosed space in which a feed reel 16 and takeup reel 18 are held in place. 20 is a length of magnetic tape, which is unwound during recording or playback from the feed reel 16 to be wound on the takeup reel 18. The passageway for the magnetic tape 20 extends from openings formed in the vicinities of the right end walls of the upper and lower half housing parts 10, 11 to openings in the vicinities of the left end walls of the same parts, through the space at the front of the front openings of these parts. A conventionally provided lid is a front lid 14, which covers the front side of the magnetic tape 20. 24 is an inner lid newly associated with the front lid 14. It covers the back side of the magnetic tape to provide protection against the ingress of dust and dirt into the housing from the front bottom thereof. A tape cassette of this character is, of course, equipped with reel brakes (not shown), or means for keeping stoppers at work to prevent unwinding of the tape due to unintentional turning of reels while the cassette is not in use as when being transported and for taking off the brakes when the cassette is used.
FIG. 3 shows one of the tape cassette reels in detail, as a bottom view (A) and a sectional view (B) taken along the line C--C' of (A). In these views, 26 is a reel hub which serves as a core of the magnetic tape. 28 is a center opening of the hub 26. Along the circumference of the center opening 28, there are equidistantly provided a plurality of, say six, inwardly projecting driven ribs 30 (i.e., 30a, 30b, 30c, 30d, 30e, and 30f) of the same contour, e.g., of an elongate, truncated pyramidal shape. When the cassette is set on a deck, drive spindles (not shown) drivably engage the ribs to transmit driving forces to the ribs. The longitudinal directions of the driven ribs 3 are closely in parallel with the centerline 32 of the center opening 28 of the particular hub. Reel flanges, indicated at 32, keep the magnetic tape properly on the hubs.
FIG. 4 shows two types of the driven ribs in fragmentary enlarged views of their end portions. The two types are characterized by their configurations shown in sets of upper and lower views (A and C) and (B and D). In each set, the upper view is of the driven rib as seen from the inside of the center opening of the hub, and the lower view is of the rib as seen from below its bottom. In the set of views (A and C), 34 is an upper face, 36 (36a, 36b) is a set of inclined side faces, left and right, and 38 (38a, 38b) is a set of inclined end faces, left and right, dividing the lower end portion into two equal planes. In the set of views (B and D), 40 is an upper face, 42 (42a, 42b) is a set of inclined side faces, left and right, and 44 is an end bevel. The mere end bevel 44 and the inclined end faces 38 differ in the angle of inclination to the surrounding wall of the hub opening. The inclined faces have a greater inclination angle each than the end face that has resulted from mere beveling.
When such a tape cassette is set on a deck, the reel brakes are released, allowing the feed and takeup reels to revolve freely. In the center hub opening 28, formed with the driven ribs 30, of each reel is fitted one of the reel drive spindles (not shown) of the deck. At this point, the lid turns through an angle of 90 deg. under the urging of a spring to expose part of the magnetic tape at the front opening of the cassette housing. At the time of setting, in the manner described, the reel drive spindles drivingly engage the center hub openings 28 of the reels almost synchronously with the release of the reel brakes. The engagement brings drive ribs (not shown) projecting sidewise from the reel drive spindles into contact with the driven ribs 30 projecting inwardly from the center openings of the hubs. Here arises a problem from the fact that the ends of the driven ribs 30 engaged with the drive ribs are either mere bevels 44 or pairs of laterally symmetrically inclined faces 44 as described above and the driven ribs 30 resting on the drive ribs are slidable and movable in either direction. Nevertheless, the brakes are on the reel drive spindles of the deck. This sometimes causes the magnetic tape wound on the feed and/or takeup reel to loosen and slack at the front opening of the cassette housing. If the cassette with the slack tape is unloaded from the deck without being wound back, the lid in the closing motion can take a "bite" of the slack tape between itself and the upper and lower half parts of the housing. This tape "bite" problem is more serious with video tape cassettes that include the front lid 14, inner lid 24, and other components.